The present invention is directed to a method and apparatus for determining bulk material properties of elastomeric materials. Further, the present invention is directed to a method and apparatus for measuring the change in pressure in an elastomeric material due to an applied force for determining the ratio of shear modulus to bulk modulus and Poisson""s ratio for the elastomeric material.
Elastomers and gel-like polymers are widely used as sealants, damping materials, or structural elements, and the like. Bulk material properties such as the bulk modulus, the shear modulus, and Poisson""s ratio are important properties in polymer engineering. Once these properties are determined, the mechanical properties of the elastomeric material may be determined. The mechanical design and application of an elastomeric material will often depend on its bulk material properties.
The experimental determination of elastomeric material properties is known to be a delicate and difficult task. Some procedures for measuring material properties involve measuring the change in volume of the elastomeric material. These measurements are often needed to four or more significant digits. This accuracy typically requires expensive instrumentation, such as a highly sensitive extensometer or precise optical measurement apparatus, to measure the slight volume change. These experimental procedures are prone to error due to the very small volume change in the elastomeric materials. Further, voids which are inevitable in polymers greatly influence any measured volume change.
There is a need for a method and apparatus that provides improved accuracy and reproducibility for measuring the bulk material properties of an elastomeric material.
Accordingly, the present invention is directed to a method for measuring bulk material properties of an elastomeric material. The method includes applying pressure to an elastomeric material in a container, measuring the pressure of the elastomeric material from a signal generated by a pressure sensor in the container, and determining a bulk material property for the elastomeric material using the signal from the pressure sensor and the magnitude of the applied pressure. The bulk material property may include Poisson""s ratio and the ratio of shear modulus to bulk modulus.
The method may include determining the coefficient of thermal expansion for the elastomeric material from the determined bulk material property. Further, the method may include the steps of adding a diluent to the elastomeric material, and determining the coefficient of diluent expansion for the elastomeric material from the change in bulk material property as a function of diluent addition.
The method of the present invention may also include the step of comparing the determined bulk material property of the elastomeric material with a known or desired bulk material property.
The present invention also includes an apparatus for determining a bulk material property of an elastomeric material. The apparatus includes a container having a cavity adapted to hold an elastomeric material and a means for applying pressure to an elastomeric material contained in the cavity. The apparatus also includes a pressure sensor in the cavity adapted to measure the pressure of the elastomeric material, and a means for determining a bulk material property of the elastomeric material in communication with the pressure sensor. The means for determining a bulk material property of the elastomeric material uses the measured pressure from the pressure sensor and the applied pressure to determine the bulk material property. The bulk material property may include Poisson""s ratio and the ratio of shear modulus to bulk modulus. The container may be made of steel, aluminum or the like. The cavities are preferably cylindrical and have a height greater than the radius of the cavity.
The apparatus may include an applied pressure sensor in the cavity adapted to measure the applied pressure. Further an environmental chamber surrounding the container wherein the environmental chamber controls the temperature of the container may also be included in the apparatus.
Still further, the apparatus may include a diluent addition source in communication with the cavity of the container that is adapted to add a diluent to the elastomeric material. The diluent may include air, gas, hydrocarbon gases, organic gases, liquids, hydrocarbon liquids, organic liquids, or combinations thereof.
The apparatus may include a means for determining the coefficient of thermal expansion for the elastomeric material from a change in the bulk material property as a function of temperature. The means for determining the coefficient of thermal expansion may be an electronic device.
The means for applying pressure to the elastomeric material may include a pressure chamber above the cavity. Further, the means for applying pressure to the elastomeric material may be a piston adapted to be slidably received in the cavity of the container.
The means for determining a bulk material property of the elastomeric material may include an electronic device such as a computer or handheld device.
The apparatus may also include a plurality of cavities in the container and a pressure sensor for each of the plurality of cavities. The geometric configuration for each cavity may be the same or different from one another.
The present invention also includes an impact force sensor. The force sensor includes a sealed container having an elastomeric material with known bulk material properties contained therein and an air chamber in the sealed container located above the elastomeric material. The force sensor also includes a first pressure sensor in the air chamber adapted to measure the pressure in the air chamber and a second pressure sensor in the container adapted to measure the pressure of the elastomeric material. A means for determining an impact force when the sensor is subjected to an impact is positioned in communication with the first and second pressure sensors. The means for determining an impact force uses the measured pressures between the first and second pressure sensors and the known bulk material constant of the elastomeric material to determine the impact force. The means for determining an impact force may include an electronic device.
Still further, the present invention includes an apparatus for determining a bulk material property of a polymer with temperature compensation. The apparatus includes a first container having a cavity adapted to hold an elastomeric material and a means for applying pressure to an elastomeric material contained in the first cavity. Also included is a first pressure sensor in the first cavity adapted to measure the pressure of the elastomeric material and a second container having a cavity adapted to hold the elastomeric material. A second pressure sensor is located in the second cavity and is adapted to measure the pressure of the elastomeric material. A means for determining a bulk material property of the elastomeric material is in communication with the first and second pressure sensors and uses the measured pressures from the first and second pressure sensors and the applied pressure to determine the bulk material property of the elastomeric material. The bulk material property may include Poisson""s ratio or the ratio of shear modulus to bulk modulus.